U.S. patent application number 14/438025 was filed with the patent office on 2015-10-08 for cathode active material for lithium secondary battery and method for manufacturing the same.
This patent application is currently assigned to LG Chem, Ltd.. The applicant listed for this patent is LG CHEM, LTD.. Invention is credited to Hye-Lim Jeon, Chi-Ho Jo, Wang-Mo Jung, Min-Suk Kang, Woo-Yeon Kong, Myung-Ki Lee, Geun-Gi Min, Sun-Sik Shin.
Application Number | 20150287984 14/438025 |
Document ID | / |
Family ID | 52676013 |
Filed Date | 2015-10-08 |
United States Patent
Application |
20150287984 |
Kind Code |
A1 |
Kong; Woo-Yeon ; et
al. |
October 8, 2015 |
CATHODE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY AND METHOD
FOR MANUFACTURING THE SAME
Abstract
The present disclosure relates to a cathode active material for
a lithium secondary battery with improved rate characteristics in
which a spinel surface structure is formed by fluorine coating on a
surface of layered lithium nickel-manganese-cobalt cathode active
material and a method for manufacturing the same, and according to
the present disclosure, there is provided a lithium secondary
battery with improved rate characteristics that may be charged to a
capacity close to a full charge in a short time when compared to a
related art and thus is suitable for high capacity of a secondary
battery.
Inventors: |
Kong; Woo-Yeon; (Daejeon,
KR) ; Lee; Myung-Ki; (Daejeon, KR) ; Kang;
Min-Suk; (Daejeon, KR) ; Shin; Sun-Sik;
(Daejeon, KR) ; Jeon; Hye-Lim; (Daejeon, KR)
; Jo; Chi-Ho; (Daejeon, KR) ; Min; Geun-Gi;
(Daejeon, KR) ; Jung; Wang-Mo; (Daejeon,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG CHEM, LTD. |
Seoul |
|
KR |
|
|
Assignee: |
LG Chem, Ltd.
Seoul
KR
|
Family ID: |
52676013 |
Appl. No.: |
14/438025 |
Filed: |
June 18, 2014 |
PCT Filed: |
June 18, 2014 |
PCT NO: |
PCT/KR2014/005375 |
371 Date: |
April 23, 2015 |
Current U.S.
Class: |
429/223 ; 427/58;
429/224 |
Current CPC
Class: |
C01P 2004/03 20130101;
Y02E 60/10 20130101; H01M 4/0421 20130101; H01M 4/366 20130101;
H01M 4/0419 20130101; C01P 2006/40 20130101; H01M 2004/028
20130101; H01M 4/1315 20130101; H01M 2004/021 20130101; H01M 4/1391
20130101; H01M 4/505 20130101; H01M 4/13915 20130101; Y02P 70/54
20151101; C01G 53/50 20130101; C01P 2002/20 20130101; C01P 2004/80
20130101; H01M 4/525 20130101; H01M 4/131 20130101; Y02E 60/122
20130101; Y02P 70/50 20151101; H01M 4/139 20130101; H01M 2220/20
20130101; H01M 4/0471 20130101; H01M 10/052 20130101 |
International
Class: |
H01M 4/36 20060101
H01M004/36; H01M 4/04 20060101 H01M004/04; H01M 4/525 20060101
H01M004/525; H01M 4/13915 20060101 H01M004/13915; H01M 4/1315
20060101 H01M004/1315; H01M 4/505 20060101 H01M004/505 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 18, 2013 |
KR |
10-2013-0069947 |
Jun 18, 2014 |
KR |
10-2014-0074346 |
Claims
1. A lithium nickel-manganese-cobalt cathode active material for a
lithium secondary battery, wherein the lithium
nickel-manganese-cobalt cathode active material has a layered
structure and a fluorine-coated surface, and the fluorine-coated
surface has a spinel-like phase.
2. The lithium nickel-manganese-cobalt cathode active material for
a lithium secondary battery according to claim 1, wherein the
lithium nickel-manganese-cobalt cathode active material is
represented by the following general formula 1:
Li.sub.xNi.sub.yMn.sub.zCo.sub.1-y-zO.sub.2 [General Formula 1]
where z>y, z>1-y-z.gtoreq.0, and x.gtoreq.1.
3. The lithium nickel-manganese-cobalt cathode active material for
a lithium secondary battery according to claim 1, wherein the
lithium nickel-manganese-cobalt cathode active material is
represented by the following general formula 2:
Li.sub.xNi.sub.yMn.sub.zCo.sub.1-y-zM.sub..alpha.O.sub.2 [General
Formula 2] where z>y, z>1-y-z.gtoreq.0, x.gtoreq.1,
0.ltoreq..alpha..ltoreq.1, and M is at least one metal selected
from the group consisting of B, Li, Mg, Al, Ca, Sr, Cr, V, Ti, Fe,
Co, Ni, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, and combinations
thereof.
4. The lithium nickel-manganese-cobalt cathode active material for
a lithium secondary battery according to claim 2, wherein
z.gtoreq.0.5.
5. The lithium nickel-manganese-cobalt cathode active material for
a lithium secondary battery according to claim 1, wherein the
lithium nickel-manganese-cobalt cathode active material has a grain
size of a longest diameter from 20 nm to 200 .mu.m.
6. The lithium nickel-manganese-cobalt cathode active material for
a lithium secondary battery according to claim 1, wherein the
fluorine-coated surface has a thickness from 2 nm to 20 .mu.m.
7. The lithium nickel-manganese-cobalt cathode active material for
a lithium secondary battery according to claim 1, wherein a z/y
value representing an Mn/Ni atomic ratio in the general formula 1
is 1<z/y.ltoreq.20.
8. The lithium nickel-manganese-cobalt cathode active material for
a lithium secondary battery according to claim 1, wherein the
fluorine coating is made by a compound selected from the group
consisting of polyvinylidene fluoride (PVdF), AlF.sub.3, NH.sub.4F,
CsF, KF, LiF, NaF, RbF, TiF, AgF, AgF.sub.2, BaF.sub.2, CaF.sub.2,
CuF.sub.2, CdF.sub.2, FeF.sub.2, HgF.sub.2, Hg.sub.2F.sub.2,
MnF.sub.2, MgF.sub.2, NiF.sub.2, PbF.sub.2, SnF.sub.2, SrF.sub.2,
XeF.sub.2, ZnF.sub.2, AlF.sub.2, BF.sub.3, BiF.sub.3, CeF.sub.3,
CrF.sub.3, DyF.sub.3, EuF.sub.3, GaF.sub.3, GdF.sub.3, FeF.sub.3,
HoF.sub.3, InF.sub.3, LaF.sub.3, LuF.sub.3, MnF.sub.3, NdF.sub.3,
VOF.sub.3, PrF.sub.3, SbF.sub.3 ScF.sub.3, SmF.sub.3, TbF.sub.3,
TiF.sub.3, TmF.sub.3, YF.sub.3, YbF.sub.3, TIF.sub.3, CeF.sub.4,
GeF.sub.4, HfF.sub.4, SiF.sub.4, SnF.sub.4, TiF.sub.4, VF.sub.4,
ZrF.sub.4, NbF.sub.5, SbF.sub.5, TaF.sub.5, BiF.sub.5, MoF.sub.6,
ReF.sub.6, SF.sub.6, WF.sub.6, fluorine-containing gas, and
mixtures thereof.
9. A method for manufacturing a lithium nickel-manganese-cobalt
cathode active material for a lithium secondary battery, the method
comprising: (a) uniformly mixing a nickel compound, a manganese
compound, and cobalt compound; (b) adding a lithium compound to a
resultant of (a) and performing a baking treatment to obtain a
layered lithium nickel-manganese-cobalt cathode active material;
and (c) coating fluorine on a surface of the layered lithium
nickel-manganese-cobalt cathode active material so that the
fluorine coated surface has a spinel-like phase.
10. The method for manufacturing a lithium nickel-manganese-cobalt
cathode active material for a lithium secondary battery according
to claim 9, wherein the fluorine coating is performed by a solid
state reaction method using heat treatment, a spray drying method,
or a vapor reaction method.
11. A cathode for a lithium secondary battery, manufactured from a
cathode mix slurry including a lithium nickel-manganese-cobalt
cathode active material for a lithium secondary battery according
to claim 1.
12. A lithium secondary battery comprising: a cathode, an anode, a
separator interposed between the cathode and the anode, and an
electrolyte solution, wherein the cathode is a cathode for a
lithium secondary battery according to claim 11.
13. A battery module comprising a lithium secondary battery
according to claim 12 as a unit cell.
14. A battery pack comprising a battery module according to claim
13 as a power source of a medium and large-sized device.
15. The battery pack according to claim 14, wherein the medium and
large-sized device is an electric vehicle, a hybrid electric
vehicle, a plug-in electric vehicle, or an energy storage
system.
16. The lithium nickel-manganese-cobalt cathode active material for
a lithium secondary battery according to claim 3, wherein
z.gtoreq.0.5.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a cathode active material
for a lithium secondary battery and a method for manufacturing the
same, and more particularly, to a cathode active material for a
lithium secondary battery with improved rate characteristics and a
method for manufacturing the same.
[0002] The present application claims priority to Korean Patent
Application No. 10-2013-0069947 filed in the Republic of Korea on
Jun. 18, 2013 and Korean Patent Application No. 10-2014-0074346
filed in the Republic of Korea on Jun. 18, 2014, the disclosures of
which are incorporated herein by reference.
BACKGROUND ART
[0003] With the technology development and the growing demands for
mobile devices, the demand for secondary batteries as an energy
source is dramatically increasing, and among the secondary
batteries, a lithium secondary battery having high energy density
and operating potential, a long cycle life, and a low
self-discharging rate has been commercialized and is being widely
used.
[0004] Also, recently, with the growing interest in environmental
issues, many studies are being conducted on electric vehicles (EVs)
and hybrid electric vehicles (HEVs) other than vehicles running on
fossil fuels, such as gasoline vehicles and diesel vehicles,
attributable to air pollution.
[0005] Electric vehicles (EVs) and hybrid electric vehicles (HEVs)
use Ni-MH secondary batteries or lithium secondary batteries having
a high energy density, a high discharge voltage and output
stability as a power source, and when a lithium secondary battery
is used in an electric vehicle, the lithium secondary battery needs
to be used for ten or more years under a severe condition along
with a high energy density and capability of providing a high
output in a short time, and thus is necessarily required to have
much better stability and long-term life characteristics than an
existing small-sized lithium secondary battery. Also, a secondary
battery in use for an electric vehicle (EV) and a hybrid electric
vehicle (HEV) needs to be excellent in rate characteristics and
power characteristics based on an operating condition of the
vehicle.
[0006] Currently, as a cathode active material of a lithium ion
secondary battery, lithium-containing cobalt oxide such as
LiCoO.sub.2 of a layered structure, lithium-containing nickel oxide
such as LiNiO.sub.2 of a layered structure, and lithium-containing
manganese oxide such as LiMn.sub.2O.sub.4 of a spinel crystal
structure are being used.
[0007] LiCoO.sub.2 has excellent material properties including
excellent cycle characteristics and is being widely used at
present, but has low safety and because cobalt as a raw material is
a finite resource, is costly and insufficient to use in large
amounts as a power source in the field of industries such as
electric vehicles. According to characteristics of a manufacturing
method, applying LiNiO.sub.2 to a mass production process at a
reasonable cost is impractical.
[0008] In contrast, lithium manganese oxide such as LiMnO.sub.2 and
LiMn.sub.2O.sub.4 has an advantage of using manganese noted for an
abundant and eco-friendly resource as a raw material, and thus is
attracting much attention as an alternative cathode active material
to LiCoO.sub.2. However, these exemplary lithium manganese oxides
have also a shortcoming of poor cycle characteristics. LiMnO.sub.2
has a drawback of low initial capacity and in that several tens of
charging and discharging cycles are needed until it reaches a
predetermined capacity. Also, LiMn.sub.2O.sub.4 experiences a
serious capacity reduction during cycles, and particularly, has a
disadvantage of drastic degradation in cycle characteristics due to
decomposition of an electrolyte solution and manganese release at
high temperature higher than or equal to 50.degree. C.
[0009] In this context, lithium nickel-manganese-cobalt-based
composite oxide of a layered structure is proposed as a good active
material having excellent battery performance balance while
overcoming or minimizing the problems of each cathode active
material. However, lithium nickel-manganese-cobalt-based composite
oxide of a layered structure needs improvements of, in particular,
rate characteristics for a wide range of applications.
DISCLOSURE
Technical Problem
[0010] The present disclosure is designed to solve the problem of
the related art, and therefore, the present disclosure is directed
to providing a lithium nickel-manganese-cobalt cathode active
material for a lithium secondary battery with improved rate
characteristics.
[0011] Also, the present disclosure is directed to providing a
method for manufacturing the above cathode active material.
Technical Solution
[0012] According to an aspect of the present disclosure, there is
provided a lithium nickel-manganese-cobalt cathode active material
for a lithium secondary battery, wherein the lithium
nickel-manganese-cobalt cathode active material has a layered
structure and a fluorine-coated surface, and the fluorine-coated
surface has a spinel-like phase.
[0013] The lithium nickel-manganese-cobalt cathode active material
may be any cathode active material having a composition higher than
or equal to 50 wt % of Mn among nickel, manganese, and cobalt, and
its non-limiting example may be represented by the following
general formula 1, but is not limited thereto:
Li.sub.xNi.sub.yMn.sub.xCo.sub.1-y-zO.sub.2 [General Formula 1]
[0014] where z>y, z>1-y-z.gtoreq.0, and x.gtoreq.1.
[0015] Alternatively, a non-limiting example of the lithium
nickel-manganese-cobalt cathode active material may be represented
by the following general formula 2:
Li.sub.xNi.sub.yMn.sub.zCo.sub.1-y-zM.sub..alpha.O.sub.2 [General
Formula 2]
[0016] where z>y, z>1-y-z.gtoreq.0, x.gtoreq.1,
0.ltoreq..alpha..ltoreq.1, and M is at least one metal selected
from the group consisting of B, Li, Mg, Al, Ca, Sr, Cr, V, Ti, Fe,
Co, Ni, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, and combinations
thereof.
[0017] In the above formula, z.gtoreq.0.5.
[0018] The lithium nickel-manganese-cobalt cathode active material
may have a secondary grain size of a longest diameter from 20 nm to
200 .mu.m.
[0019] The fluorine-coated surface may have a thickness from 2 nm
to 20 .mu.m.
[0020] In the general formula 1, a z/y value representing an Mn/Ni
atomic ratio may be 1<z/y.ltoreq.20.
[0021] The fluorine coating may be made by a compound selected from
the group consisting of polyvinylidene fluoride (PVdF), AlF.sub.3,
NH.sub.4F, CsF, KF, LiF, NaF, RbF, TiF, AgF, AgF.sub.2, BaF.sub.2,
CaF.sub.2, CuF.sub.2, CdF.sub.2, FeF.sub.2, HgF.sub.2,
Hg.sub.2F.sub.2, MnF.sub.2, MgF.sub.2, NiF.sub.2, PbF.sub.2,
SnF.sub.2, SrF.sub.2, XeF.sub.2, ZnF.sub.2, AlF.sub.2, BF.sub.3,
BiF.sub.3, CeF.sub.3, CrF.sub.3, DyF.sub.3, EuF.sub.3, GaF.sub.3,
GdF.sub.3, FeF.sub.3, HoF.sub.3, InF.sub.3, LaF.sub.3, LuF.sub.3,
MnF.sub.3, NdF.sub.3, VOF.sub.3, PrF.sub.3, SbF.sub.3 ScF.sub.3,
SmF.sub.3, TbF.sub.3, TiF.sub.3, TmF.sub.3, YF.sub.3, YbF.sub.3,
TIF.sub.3, CeF.sub.4, GeF.sub.4, HfF.sub.4, SiF.sub.4, SnF.sub.4,
TiF.sub.4, VF.sub.4, ZrF.sub.4, NbF.sub.5, SbF.sub.5, TaF.sub.5,
BiF.sub.5, MoF.sub.6, ReF.sub.6, SF.sub.6, WF.sub.6,
fluorine-containing gas, and mixtures thereof.
[0022] According to another aspect of the present disclosure, there
is provided a method for manufacturing a lithium
nickel-manganese-cobalt cathode active material for a lithium
secondary battery, including (a) uniformly mixing a nickel
compound, a manganese compound, and cobalt compound, (b) adding a
lithium compound to a resultant of (a) and performing a baking
treatment to obtain a layered lithium nickel-manganese-cobalt
cathode active material, and (c) coating fluorine on a surface of
the layered lithium nickel-manganese-cobalt cathode active material
so that the fluorine coated surface has a spinel-like phase.
[0023] The fluorine coating may be performed by a solid state
reaction method using heat treatment, a spray drying method, or a
vapor reaction method.
[0024] According to another aspect of the present disclosure, there
is provided a cathode for a lithium secondary battery manufactured
from a cathode mix slurry including the above lithium
nickel-manganese-cobalt cathode active material for a lithium
secondary battery.
[0025] According to another aspect of the present disclosure, there
is provided a lithium secondary battery including a cathode, an
anode, a separator interposed between the cathode and the anode,
and an electrolyte solution, wherein the cathode is the above
cathode for a lithium secondary battery.
[0026] According to another aspect of the present disclosure, there
is provided a battery module including the above lithium secondary
battery as a unit cell.
[0027] According to another aspect of the present disclosure, there
is provided a battery pack including the above battery module as a
power source of a medium and large-sized device.
[0028] The medium and large-sized device may be an electric
vehicle, a hybrid electric vehicle, a plug-in electric vehicle, or
an energy storage system.
Advantageous Effects
[0029] According to the present disclosure, a lithium secondary
battery with improved rate characteristics that may be charged to a
capacity close to a full charge in a short time when compared to a
related art is provided. The lithium secondary battery is adequate
for high capacity and suitable for use as a power source of a
medium- or large-sized device.
DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1a is a scanning electron microscope (SEM) image of a
cathode active material according to Embodiment example 1, and FIG.
1b is an SEM image of a cathode active material according to
Comparative example 1.
[0031] FIGS. 2a and 2b are discharge capacity vs cycle number
graphs of lithium secondary batteries according to Embodiment
example 2 and Comparative example 2, respectively.
[0032] FIG. 3 is a rate capability vs C-rate graph for each of
lithium secondary batteries according to Embodiment example 2 and
Comparative example 2.
BEST MODE FOR CARRYING OUT THE INVENTION
[0033] Hereinafter, the present disclosure will be described in
detail. It should be understood that the terms used in the
specification and the appended claims should not be construed as
limited to general and dictionary meanings, but interpreted based
on the meanings and concepts corresponding to technical aspects of
the present disclosure on the basis of the principle that the
inventor is allowed to define terms appropriately for the best
explanation.
[0034] A layered lithium nickel-manganese-cobalt cathode active
material of the present disclosure is surface-coated with
fluorine.
[0035] The layered lithium nickel-manganese-cobalt cathode active
material may be any cathode active material having a composition
higher than or equal to 50 wt % of Mn among nickel, manganese, and
cobalt, and its non-limiting example may be represented by the
following general formula 1, but is not limited thereto.
Li.sub.xNi.sub.yMn.sub.zCo.sub.1-y-zO.sub.2 [General Formula 1]
[0036] where z>y, z>1-y-z.gtoreq.0, x.gtoreq.1.
[0037] In the general formula 1, a z/y value representing a Mn/Ni
atomic ratio is preferably 1<z/y.ltoreq.20. When the z/y value
is higher than the upper limit, safety may significantly reduce,
and when the z/y value is lower than the lower limit, it is
difficult to expect a high capacity.
[0038] Alternatively, a non-limiting example of the layered lithium
nickel-manganese-cobalt cathode active material according to an
aspect of the present disclosure may be represented by the
following general formula 2:
Li.sub.xNi.sub.yMn.sub.zCo.sub.1-y-zM.sub..alpha.O.sub.2 [General
Formula 2]
[0039] where z>y, z>1-y-z.gtoreq.0, x.gtoreq.1,
0<.alpha..ltoreq.1, and M is at least one metal selected from
the group consisting of B, Li, Mg, Al, Ca, Sr, Cr, V, Ti, Fe, Co,
Ni, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, and combinations thereof.
[0040] Also, a z/y value representing a Mn/Ni atomic ratio is
preferably 1<z/y.ltoreq.20.
[0041] Also, in the above general formulas 1 and 2, z.gtoreq.0.5 is
preferred.
[0042] The lithium nickel-manganese-cobalt cathode active material
may have a grain size of a longest diameter from 20 nm to 200
.mu.m, but is not limited thereto.
[0043] The fluorine coating is applied to the surface of the
layered lithium nickel-manganese-cobalt cathode active material,
namely, a target material for coating, to create a reducing
environment when baking so that the surface of the cathode active
material may form a spinel-like phase. In regards to this,
reference is made to FIGS. 1a and 1b; FIG. 1a is a scanning
electron microscope (SEM) image of a fluorine-coated cathode active
material according to an aspect of the present disclosure, and FIG.
1b is an SEM image of the cathode active material before fluorine
coating, and in the SEM images, the lithium nickel-manganese-cobalt
cathode active material has a flake form. Generally, a surface
structure of dot form or other form appears on the surface of a
cathode active material after fluorine coating, but the lithium
nickel-manganese-cobalt cathode active material according to an
aspect of the present disclosure has an advantage of being less
attacked from an electrolyte solution because a protective coating
is formed by a uniform or nearly uniform fluorine coating provided
on the cathode active material particles.
[0044] A principle of forming the spinel-like phase by applying
fluorine onto the surface of the layered cathode active material of
General Formula 1 is not yet clarified, but is figured out by
experiment results. Moreover, by the fluorine coating of the
cathode active material, the influence on acid produced near the
cathode active material decreases, or reactivity of the cathode
active material with an electrolyte solution is suppressed, so a
phenomenon in which the battery capacity drastically reduces may be
resolved, and consequently, charging/discharging characteristics,
life characteristics, a high voltage and high rate characteristics,
and thermal safety may be improved. In particular, the cathode
active material having the spinel-like phase surface structure
according to an aspect of the present disclosure is advantageous in
improving the rate characteristics, compared to a cathode active
material having gone through fluorine coating without modifying a
surface structure.
[0045] Examples of fluorine containing compounds used in the
fluorine coating include, but are not limited to, polyvinylidene
fluoride (PVdF), AlF.sub.3, NH.sub.4F, CsF, KF, LiF, NaF, RbF, TiF,
AgF, AgF.sub.2, BaF.sub.2, CaF.sub.2, CuF.sub.2, CdF.sub.2,
FeF.sub.2, HgF.sub.2, Hg.sub.2F.sub.2, MnF.sub.2, MgF.sub.2,
NiF.sub.2, PbF.sub.2, SnF.sub.2, SrF.sub.2, XeF.sub.2, ZnF.sub.2,
AlF.sub.2, BF.sub.3, BiF.sub.3, CeF.sub.3, CrF.sub.3, DyF.sub.3,
EuF.sub.3, GaF.sub.3, GdF.sub.3, FeF.sub.3, HoF.sub.3, InF.sub.3,
LaF.sub.3, LuF.sub.3, MnF.sub.3, NdF.sub.3, VOF.sub.3, PrF.sub.3,
SbF.sub.3 ScF.sub.3, SmF.sub.3, TbF.sub.3, TiF.sub.3, TmF.sub.3,
YF.sub.3, YbF.sub.3, TIF.sub.3, CeF.sub.4, GeF.sub.4, HfF.sub.4,
SiF.sub.4, SnF.sub.4, TiF.sub.4, VF.sub.4, ZrF.sub.4, NbF.sub.5,
SbF.sub.5, TaF.sub.5, BiF.sub.5, MoF.sub.6, ReF.sub.6, SF.sub.6,
WF.sub.6, and fluorine-containing gas.
[0046] The fluorine coated surface may have a thickness from 2 nm
to 20 .mu.m or from 2 nm to 5 .mu.m, but is not limited thereto.
When the fluorine coated surface is thinner than the lower limit, a
spinel-like phase may not be properly formed, and when the fluorine
coated surface is thicker than the upper limit, movement of Li ions
may be unfavorable and many side reactions with an electrolyte
solution may occur.
[0047] Also, the content of the fluorine coating may be from 0.01
to 8 wt % or from 0.01 to 5 wt % based on the weight of the cathode
active material. When the content of the fluorine coating is less
than the lower limit, modification to a layered spinel-like phase
structure is not made on the surface of the cathode active
material, and when the content of the fluorine coating is in excess
beyond the upper limit, a relative ratio of the cathode active
material reduces and a capacity or energy density reduces.
[0048] A method for manufacturing lithium
nickel-manganese-cobalt-based composite oxide for a lithium
secondary battery according to the present disclosure may include,
but is not limited to the following steps of:
[0049] (a) uniformly mixing a nickel compound, a manganese
compound, and cobalt compound;
[0050] (b) adding a lithium compound to a resultant of (a) and
performing a baking treatment to obtain a layered lithium
nickel-manganese-cobalt cathode active material; and
[0051] (c) coating fluorine on the surface of the layered lithium
nickel-manganese-cobalt cathode active material so that the
fluorine coated surface has a spinel-like phase.
[0052] The nickel compound may include, for example, Ni(OH).sub.2,
NiO, NiOOH, NiCO.sub.3.2Ni(OH).sub.2.4H.sub.2O,
NiC.sub.2O.sub.4.2H.sub.2O, Ni(NO.sub.3).sub.2.6H.sub.2O,
NiSO.sub.4, NiSO.sub.4.6H.sub.2O, nickel salt of fatty acid, and
nickel halide. Among them, a nickel compound not including a
nitrogen or sulfur atom during baking treatment, such as
Ni(OH).sub.2, NiO, NiOOH, NiCO.sub.30.2Ni(OH).sub.2.4H.sub.2O, and
NiC.sub.2O.sub.4.2H.sub.2O, is preferred in that it does not
produce a harmful substance such as NO.sub.x and SO.sub.x during a
baking process. Such nickel compounds may be used singularly or in
combination.
[0053] The manganese compound may include, for example, manganese
oxide such as Mn.sub.2O.sub.3, MnO.sub.2, and Mn.sub.3O.sub.4,
MnCO.sub.3, Mn(NO.sub.3).sub.2, MnSO.sub.4; manganese salt such as
manganese acetate, manganese(II) dicarboxylate, manganese citrate,
and manganese salt of fatty acid; and halide such as manganese
chloride. Among them, MnO.sub.2, Mn.sub.2O.sub.3, and
Mn.sub.3O.sub.4 are preferred, and this is because they are
available as an industrial raw material at a low cost while not
producing No.sub.x and SO.sub.x and gas such as CO.sub.2 during
baking treatment. Such manganese compounds may be used singularly
or in combination.
[0054] The cobalt compound may include, for example, Co(OH).sub.2,
CoOOH, CoO, CO.sub.2O.sub.3, Co.sub.3O.sub.4,
Co(OCOCH.sub.3).sub.2.4H.sub.2O, CoCl.sub.2,
Co(NO.sub.3).sub.2.6H.sub.2O, and Co(SO.sub.4).sub.2.7H.sub.2O.
Among them, Co(OH).sub.2, CoOOH, CoO, Co.sub.2O.sub.3, and
Co.sub.3O.sub.4 are preferred in that they do not produce a harmful
substance such as NO.sub.x and SO.sub.x during baking treatment.
Co(OH).sub.2 and CoOOH are more preferred from the perspective of a
low cost in the industrial aspect and high reactivity. Such cobalt
compounds may be used singularly or in combination.
[0055] A method of mixing the raw materials is not limited to a
particular one, and the raw materials may be mixed by a wet or dry
process. For example, a method using a machine such as a ball mill,
a vibratory mill, and a bead mill may be contemplated. The wet
mixing is preferred because it allows for more uniform mixing and
increased reactivity of a mixture in a baking process.
[0056] A mixing time may change based on a mixing method. However,
so long as the raw materials are uniformly mixed at a particulate
level, any mixing time may be used. For example, when mixing using
a ball mill (wet or dry mixing), a mixing time is generally from
about 1 hour to about two days, and when mixing using a bead mill
(wet continuous method), a dwell time is generally from about 0.1
hour to about 6 hours.
[0057] After wet grinding, the particles are dried by a general
method. A drying method is not limited to a particular one.
However, in terms of uniformity of a particulate material to be
produced, powder flowability and powder processing performance, and
efficiency in forming spherical secondary particles, spray drying
is preferred.
[0058] The powder obtained by spray drying is sufficiently mixed
with lithium-containing compounds such as Li.sub.2CO.sub.3,
LiNO.sub.3, LiNO.sub.2, LiOH, LiOH.H.sub.2O, LiH, LiF, LiCl, LiBr,
LiI, CH.sub.3OOLi, Li.sub.2O, Li.sub.2SO.sub.4, lithium
dicarboxylate, lithium citrate, and lithium salt of fatty acid and
alkyl lithium.
[0059] The resulting powder mixture is baked. A baking condition is
determined based on a composition and lithium compound materials
being used. A baking temperature is generally 800.degree. C. or
higher, preferably 900.degree. C. or higher, more preferably
950.degree. C. or higher, and generally 1100.degree. C. or lower,
preferably 1075.degree. C. or lower, more preferably 1050.degree.
C. or lower.
[0060] Subsequently, a fluorine-containing compound is coated on
the surface of the lithium nickel-manganese-cobalt cathode active
material. A coating method may include, but is not limited to, for
example, a solid phase reaction which performs heat treatment on
the fluorine-containing compound and the cathode active material at
a proper temperature, a spray drying method which dissolves the
fluorine-containing compound in a solvent and disperses/sprays it,
or a vapor reaction using gas. The solid phase reaction is
advantageous in aspects of a process or costs, and may include a
process of heat treatment at 300 to 600.degree. C. for 5 to 10
hours.
[0061] The cathode active material of the present disclosure
manufactured in this way may form a cathode mix with a binder and a
conductive material generally used in the art.
[0062] The binder is a substance that aids the binding of the
cathode active material and the conductive material etc. and the
binding of the cathode active material to the current collector,
and may be added in an amount of, for example, 1 to 30 parts by
weight based on 100 parts by weight of the cathode active material,
but its content is not specially limited in the present disclosure.
The binder is not limited to a particular one, but may include, for
example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene
(PTFE), fluororubber, styrene-butadiene rubber (SBR), and
cellulose-based resin.
[0063] The conductive material may be added in an amount of, for
example, 1 to 50 parts by weight based on 100 parts by weight of
the cathode active material, but its content is not specially
limited in the present disclosure. The conductive material is not
limited to a specific type if it is conductive while not causing a
chemical change in the battery in question, and may include, for
example, a carbon black-based conductive material such as graphite
or acetylene black.
[0064] A dispersant may be selected from the group consisting of
N-methyl-2-pyrrolidone, diacetone alcohol, dimethylformaldehyde,
propyleneglycol monomethylether, methyl cellosolve, ethyl
cellosolve, butyl cellosolve, isopropyl cellosolve, acetylacetone,
methyl isobutyl ketone, n-butyl acetate, cellosolve acetate,
toluene, xylene, and mixtures thereof, but is not limited
thereto.
[0065] The cathode mix slurry is coated on a cathode current
collector and dried to form a cathode for a lithium secondary
battery.
[0066] The cathode current collector generally has a thickness from
10 to 500 .mu.m. The cathode current collector is not limited to a
specific type if it has high conductivity while not causing a
chemical change in the corresponding battery, and may be made from,
for example, stainless steel, aluminum, nickel, titanium, baked
carbon, or aluminum or stainless steel treated with carbon, nickel,
titanium, or silver on the surface.
[0067] A thickness of the cathode mix slurry on the cathode current
collector is not specially limited, and may be, for example, from
10 to 300 .mu.m, and a loading amount of active materials may be 5
to 50 mg/cm.sup.2.
[0068] According to another aspect of the present disclosure, there
is provided a lithium secondary battery including a cathode, an
anode, a separator interposed between the cathode and the anode,
and an electrolyte solution, wherein the above cathode is used as
the cathode.
[0069] Also, the lithium secondary battery may be fabricated by
manufacturing an anode, a separator, and an electrolyte solution by
a general method known in the art and assembling them with the
cathode.
[0070] A non-limiting example of an anode active material may
include a general anode active material usable in an anode of a
conventional electrochemical cell, in particular, a lithium
adsorption material such as a lithium metal or a lithium alloy,
carbon, petroleum coke, activated carbon, graphite, or other
carbons is preferred. An anode current collector may be, as a
non-limiting example, a foil made from copper, gold, nickel or
copper alloy, or combinations thereof.
[0071] For the separator, a polyolefin-based film of porous
polyethylene and porous polypropylene, an organic/inorganic
composite separator having a porous coating layer formed on a
porous substrate, a non-woven film, and engineering plastic may be
used, but is not limited thereto. As a process of applying the
separator to a battery, a lamination/stacking process and a folding
process as well as a winding process being generally used may be
contemplated.
[0072] The electrolyte solution usable in an exemplary embodiment
of the present disclosure may be an electrolyte solution in which a
salt, for example, of A.sup.+B.sup.- structure, where A.sup.+
represents an alkali metal cation such as Li.sup.+, Na.sup.+ and
K.sup.+, or combinations thereof, and B.sup.- represents an anion
such as PF.sub.6.sup.-, BF.sub.4.sup.-, Cl.sup.-, Br.sup.-,
I.sup.-, ClO.sub.4.sup.-, AsF.sub.6.sup.-, CH.sub.3CO.sub.2.sup.-,
CF.sub.3SO.sub.3.sup.-, N(CF.sub.3SO.sub.2).sub.2.sup.- and
C(CF.sub.2SO.sub.2).sub.3.sup.-, or combinations thereof, is
dissolved or dissociated in an organic solvent including, but is
not limited to, propylene carbonate (PC), ethylene carbonate (EC),
diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl
carbonate (DPC), dimethylsulfoxide, acetonitrile, dimethoxyethane,
diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP),
ethylmethylcarbonate (EMC), gamma butyrolactone, or mixtures
thereof.
[0073] Also, with an aim to improve the charging/discharging
characteristics, retardancy, and the like, pyridine,
triethylphosphite, triethanol amine, cyclic ether, ethylene
diamine, n-glyme, hexamethyl phosphoric triamide, nitrobenzene
derivatives, sulfur, quinone imine dyes, N-substituted
oxazolidinone, N,N-substituted imidazolidine, ethylene glycol
dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, and
trichloro aluminium, for example, may be added to the electrolyte
solution. According to circumstances, to impart non-flammable
properties, a halogen containing solvent such as carbon
tetrachloride and trifluoroethylene may be additionally included,
and to improve the preserving characteristics at high temperature,
carbon dioxide gas may be additionally included, and
fluoro-ethylene carbonate (FEC), propene sultone (PRS), and
fluoro-propylene carbonate (FPC) may be additionally included.
[0074] Injection of the electrolyte solution may be performed in a
proper step among a battery fabrication process based on a
manufacturing process and required physical properties of a final
product. That is, injection of the electrolyte solution may be
applied before battery assembling or in a final step of battery
assembling.
[0075] The secondary battery according to the present disclosure
may be not only used in a battery cell which may be used as a power
source of a small device, but also used as a unit battery in a
medium-large sized battery module including a plurality of battery
cells.
[0076] Also, the present disclosure provides a battery pack
including the battery module as a power source of a medium and
large-sized device, and the medium and large-sized device may be
used in an electric car including an electric vehicle (EV), a
hybrid electric vehicle (HEV), and a plug-in hybrid electric
vehicle (PHEV), an energy storage system, and the like.
MODE FOR CARRYING OUT THE INVENTION
[0077] Hereinafter, the present disclosure will be described in
detail through embodiments. The embodiments of the present
disclosure, however, may take several other forms, and the scope of
the present disclosure should not be construed as being limited to
the following embodiments. The embodiments of the present
disclosure are provided to more fully explain the present
disclosure to those having ordinary knowledge in the art to which
the present disclosure pertains.
Embodiment Example 1
Manufacture of Cathode
[0078] 100 g of layered lithium nickel-manganese-cobalt composite
oxide Li.sub.aNi.sub.0.4Mn.sub.0.6O.sub.2 (1.ltoreq.a<1.5) was
mixed with 0.3 g of a fluorine containing compound PVdF, and heat
treatment was performed at 500.degree. C. for 5 to 10 hours.
Fluorine-coated lithium nickel-manganese-cobalt composite oxide was
obtained.
[0079] Subsequently, the lithium nickel-manganese-cobalt composite
oxide was dissolved in a dispersant along with a conductive
material and a binder to obtain a slurry, and the slurry was coated
on an aluminum current collector and dried at temperature of 100 to
130.degree. C. for 2 hours, to manufacture a cathode.
Embodiment Example 2
Manufacture of Lithium Secondary Battery
[0080] The cathode obtained in Embodiment example 1 was used as a
cathode of a lithium secondary battery.
[0081] As an anode, a generally available Li metal was used.
[0082] As a separator, a polyethylene film was used, and the
separator was interposed between the cathode and the anode, a
solution including 1 mol LiPF.sub.6 in a mixed solvent
EC/DMC/EMC=3/4/3 was used as an electrolyte solution, and a battery
was manufactured by a general manufacturing method.
Comparative Example 1
Manufacture of Cathode
[0083] A cathode was manufactured by the same method as Embodiment
example 1 except non-fluorine-coated layered lithium
nickel-manganese-cobalt composite oxide was used.
Comparative Example 2
Manufacture of Lithium Secondary Battery
[0084] A lithium secondary battery was manufactured by the same
method as Embodiment example 2 except the cathode obtained in
Comparative example 1 was used.
Evaluation Example 1
Capacity and Rate Measurement of Lithium Secondary Battery
[0085] The lithium secondary batteries manufactured in Embodiment
example 2 and Comparative example 2 were charged under a condition
of current=0.1C up to 4.65V, and its capacity was measured.
Subsequently, a discharge capacity was measured at current=0.1C up
to 2.75V. These results are shown in the following Table 1.
TABLE-US-00001 TABLE 1 Embodiment Comparative example 1 example 1
First charge capacity (mAh/g) 285.8 285.3 First discharge capacity
(mAh/g) 238.0 228.9 First efficiency (%) 83.3 80.2
[0086] Also, a discharge capacity was measured at a rate of 0.1C,
0.5C, 1.0C, and 2.0C at an operating voltage from 2.75 to 4.45V. A
discharge capacity at 0.5C is shown in FIGS. 2a and 2b.
[0087] FIG. 2b is a triplicate experiment graph of a cell
fabricated by the same method using a bare cathode active material
manufactured by the same method, and it can be seen that even the
cells using the same type of cathode active material show a
significant discharge capacity difference. It is found that this
big difference has occurred because the bare sample free of
fluorine coating on the surface of the cathode active material is
susceptible to surface exposure to an electrolyte solution, leading
to a side reaction which accelerates the degradation, in
particular, an electrolyte solution side reaction occurs more
intensively at a certain partial zone of the cathode active
material.
[0088] In contrast, it can be seen from a triplicate experiment
graph, as illustrated in FIG. 2a, of the cell manufactured using
the fluorine-coated cathode active material, that a capacity
retention rate is higher than or equal to 92% even after about 50
cycles without any difference between cells. As seen in the SEM
image, uniform coating formed on the surface protects the cathode
active material well from an electrolyte solution and contributes
to slow degradation even after tens of cycles.
[0089] Also, rate capability of the battery cell exhibiting the
highest discharge capacity in Comparative example 2 and the battery
cell of Embodiment example 2 is shown in FIG. 3.
* * * * *